Teaching Organic Farming & Gardening

Appendix 4 (cont.): Side Forking or Deep Forking
Sequence

Step 2. With a gentle, side-glancing
blow, “whack” the clods until any
substantial clods are broken up and
eliminated. Work from the center of
the bed toward the path. With each
pass, center to path, slightly overlap
with the previous pass.

Step 3. With a long-handled bow rake, Unit 1.2  |  Part 1 – 87
begin to shape the bed so that it is level Tillage & Cultivation
and straight-sided. You can draw soil
from the high spots to the low spots, and
vice versa. Using both sides of the rake
(the tines and the flat/bow side), and
using both a pushing and pulling motion
will facilitate this process.

Illustrations by José Miguel Mayo

Appendix 4: Side Forking or Deep Forking Sequence

Appendix 4 (cont.): Side Forking or Deep Forking
Sequence

Step 4. You can also use the rake to “berm” or
gently pound the vertical side of the bed to
create a firm, straight edge, perpendicular to
the flat top. This helps maintain the bed’s shape.

Part 1 – 88  |  Unit 1.2  Illustration by José Miguel Mayo
Tillage & Cultivation Appendix 4: Side Forking or Deep Forking Sequence

Appendix 5: Field-Scale Tillage & Planting
Implements

3-Point Flail Mower

3-Bar Cultivator

3-Point Chisel

Lister Bar

Illustrations by Cathy Genetti Reinhard Unit 1.2  |  Part 1 – 89
Appendix 5: Field-Scale Tillage & Planting Implements Tillage & Cultivation

Appendix 5 (cont.): Field-Scale Tillage & Planting
Implements

2-Row Bed Shaper

3-Point Terracing Blade

Springtooth Harrow

Ring Roller

Part 1 – 90  |  Unit 1.2  Illustrations by Cathy Genetti Reinhard
Tillage & Cultivation Appendix 5: Field-Scale Tillage & Planting Implements

Appendix 5 (cont.): Field-Scale Tillage & Planting
Implements

KNIGHT 180 Offset Wheel Disc
Lilliston Cultivator
Manure Spreader

Illustrations by Cathy Genetti Reinhard Unit 1.2  |  Part 1 – 91
Appendix 5: Field-Scale Tillage & Planting Implements Tillage & Cultivation

Appendix 5 (cont.): Field-Scale Tillage & Planting
Implements

Mechanical Spader: A primary tillage implement used to incorporate cover crop and crop residue.
Spaders operate at a very slow speed and perform deep tillage (14+ inches) without soil inversion to
create a similar effect on soil as double digging.

Part 1 – 92  |  Unit 1.2  Illustration by José Miguel Mayo
Tillage & Cultivation Appendix 5: Field-Scale Tillage & Planting Implements

Appendix 6: Tractors & Implements for Mixed
Vegetable Farming Operations Based on
Acreage

2 to 5 acres: • three point fork lift attachment for moving harvest
• 30 HP diesel 4x4 tractor (compact utility bins etc.

configuration with decent clearance, “Ag” tires, • three point three bar cultivator with sweeps,
three point hitch, PTO, low gearing, upright knives, disc hillers etc. for cultivation of furrow
exhaust, power steering, auxiliary hydraulics etc.) bottoms and bed sides
• 5 foot three point rototiller
• double tool bar and “A” frame (5.5 feet wide) with • three point seed broadcaster for cover crop
assortment of clamps, standards, shovels, sweeps, seeding
etc.
• push planter • backpack flamer
• various hand and push cultivation tools
• single three point ripper shank capable of running 10 to 20 acres:
2 feet deep • 60 HP diesel 4x4 tractor with wide tires and
• bed shaper/marker
• three point heavy tandem disc weights for pulling discs, rippers etc.
• flail mower
• 6 foot spring-tooth cultivator • 25 to 30 HP 2 WD tractor (row crop configuration/
• box scraper high clearance, three point etc.)
• under-cutter
• three point fork lift attachment for moving harvest • 6 foot three point rototiller
bins etc. • rolling cultivator
• hand crank broadcaster for broadcasting cover • bed shaper with vegetable seeders
crop seed • three point ripper (three shank) capable of running
• backpack flamer
2 feet deep
5 to 10 acres: • off set wheel disc 7 feet wide with ring roller
• flail mower
• 40 HP diesel 4x4 tractor (row crop configuration • 8 foot spring-tooth cultivator
with good ground clearance, 12 inch wide tires, as • hydraulic wheel scraper (6 foot)
well as all the amenities mentioned above) • under-cutter
• three point fork lift attachment for moving harvest
• 6 foot three point rototiller
• double tool bar and “A” frame (6.6 feet wide) with bins etc.
• three point three bar cultivator with sweeps,
assortment of clamps standards, shovels, sweeps
• rolling cultivator knives, disc hillers etc. for cultivation of furrow
• bed shaper with vegetable seeders bottoms and bed sides
• three point ripper (two shank) capable of running • grain drill for cover crop seeding
• mechanical spading machine (6 feet wide)
2 feet deep • three point heavy tandem disc with tool bar and
• three point heavy tandem disc shovels for recycling beds
• flail mower • terracing blade for making drain ditches, etc.
• 6 foot spring-tooth cultivator
• box scraper
• under-cutter

Appendix 6: Tractors & Implements for Mixed Vegetable Farming Unit 1.2  |  Part 1 – 93
Tillage & Cultivation

Appendix 7: Tillage Pattern for O set Wheel Disc

Dead On your tight turns you can leave the disc lowered.
furrow On the broader turns you can lift the disc on the avenue
so that you can avoid making a mess of the avenue. The
Dirt goes disc will actually lift out of the ground when turning.
this way Discs were designed to be used behind draft animals.
(The pattern is exaggerated on paper).
When you are discing, all of your entry
points will be in line with the eld Each new pass (to the right of
edge and your travel on the ends your last pass) should e ectively
will be in the avenues. It is a good
idea to spade the ends since ll the dead furrow, leaving the
the disc is not e ectively eld relatively level.
cutting and mixing close
to the eld edge.

With an “o -set” disc
you only ever turn
to the left when
in the eld.

Typical discing pattern for a half-acre eld. If done properly you will have only one
“dead” furrow in the middle of the eld. Each edge will also have a “dead furrow.”

Part 1 – 94 | Unit 1.2 Illustrations by José Miguel Mayo
Tillage & Cultivation Appendix 7: Tillage Pattern for O set Wheel Disc

1.3

Propagating
Crops from Seed,
and Greenhouse
Management

Introduction 97

Lecture 1: Seed Biology, Germination, and Development: 99
Environmental Conditions and Cultural Requirements

Lecture 2: Managing Environmental Conditions— 105
Using Greenhouses to Optimize Seedling Production

Lecture 3: Heating, Cooling, Lighting, Irrigation, and 113
Climate Control Systems

Lecture 4: Soil Media, Fertility, and Container Formats 119

Demonstration 1: Greenhouse Management

Instructor’s Demonstration Outline 127

Demonstration 2: Propagation Media

Instructor’s Demonstration Outline 128

Demonstration 3: Sowing Seed

Instructor’s Demonstration Outline 129

Demonstration 4: Transplanting or “Pricking Out”

Instructor’s Demonstration Outline 130

Demonstration 5: Greenhouse Irrigation

Instructor’s Demonstration Outline 132

Demonstration 6: Seedling Development and
the “Hardening Off” Process

Instructor’s Demonstration Outline 133

Assessment Questions and Key 135

Resources 139

Supplements:

1. E xamples of Daily Cool- and Warm-Season Greenhouse 145
Management in a Passive Solar Greenhouse

2. C onserving Water and Protecting Water 148
Quality

3. L ow-Cost and Sustainable Alternatives to 149
Traditional Greenhouse Propagation

Glossary 151

Appendices

1. Characteristics of Open-Pollinated (OP) and 153
Hybrid Seed

2. Seed Viability Chart 154

3. S oil Temperature Conditions for Vegetable 155
Seed Germination

4. Days Required for Seedling Emergence at 156
Various Soil Temperatures from Seed Planted
1/2-inch Deep

5. Approximate Monthly Temperatures for 157
Best Growth and Quality of Vegetable Crops

6. Examples of Propagation Containers 158

7. Propagation Media—Ingredients and Properties 159
Imparted

8. Sample Soil Mix Recipes 160

9. “Pricking Out”Technique, Depth of Planting 161

10. Flat-Grown and Cell-Grown Seedlings 162

11. Propagation and Crop Performance Records Sheet 163

12. Greenhouse Records Sheet 164

Part 1 – 96  |  Unit 1.3 
Propagation/Greenhouse Management

Introduction: Propagation/Greenhouse
Management

UNIT OVERVIEW MODES OF INSTRUCTION

Getting plants off to a healthy > LECTURES (4 LECTURES, 1.5 HOURS EACH)
start is critical to successful crop
production. This unit introduces Lecture 1 covers seed biology, and the cultural require-
students to the basic skills, concepts, ments for germination and healthy seedling development.
and equipment associated with
the sexual propagation of crop Lecture 2 examines the rationale and associated costs and
plants, and the use of greenhouses benefits of solar and conventional greenhouse structures,
to promote healthy seedling and the prevention/management of common greenhouse
production. Lectures, exercises, pest and pathogens.
and supporting material emphasize
the roles of temperature, moisture, Lecture 3 takes a closer look at greenhouse technology:
air circulation, and fertility in heating, cooling, lighting, and irrigation systems.
germination, seedling development,
and pest and disease control. Lecture 4 addresses desirable characteristics of propaga-
tion media, common container formats, and supplemental
Four lectures examine cultural require- fertility.
ments of seeds and seedlings, as well as the
technology, costs, advantages, and disad- > DEMONSTRATION 1: GREENHOUSE MANAGEMENT
vantages of various greenhouse structures, (1–1.5 HOURS)
and options for propagation media and
container formats. A series of demonstra- The greenhouse demonstration illustrates the way that air
tions then introduces the skills involved in temperature, soil moisture, and air circulation are man-
sowing seeds and the cultural practices used aged to create optimal environmental conditions for seed
to manage passive solar greenhouses to pro- germination and seedling growth. Students will also be
mote successful development of organically introduced to the steps used to prepare seedlings for field
grown seedlings. Supplements address ex- transplanting.
amples of daily greenhouse practices, along
with ways to conserve water, protect water > DEMONSTRATIONS 2–6: PROPAGATION MEDIA, SEED
quality, and lower expenses associated with SOWING, TRANSPLANTING, IRRIGATION, AND SEEDLING
greenhouse propagation. DEVELOPMENT (1–1.5 HOURS EACH)

The propagation demonstrations illustrate the techniques
used to produce propagation media, sow seeds, transplant
seedlings, and manage irrigation and seedling development.

> ASSESSMENT QUESTIONS (0.5–1 HOUR)

Assessment questions reinforce key unit concepts and skills.

> POWERPOINT, VIDEOS

See casfs.ucsc.edu/about/publications and click on Teaching
Organic Farming & Gardening.

Introduction Unit 1.3  |  Part 1 – 97
Propagation/Greenhouse Management

LEARNING OBJECTIVES SKILLS
• How to create propagation media
CONCEPTS
• Definition of sexual propagation • How to sow seeds into flats and cell trays

• Propagation media: Components, properties and • How to manage a greenhouse/cold frame:
ratios of materials used Maintaining optimal environmental
conditions for germination and early stages of
• Containers: Advantages and disadvantages of seedling growth
commonly used formats
• How to transplant/“prick out” seedlings
• Accurate documentation of propagation for
trouble shooting • How to manage seedlings in preparation for
field transplanting
• Germination requirements of various crops:
Seed physiology, seed treatments, temperature • How to identify appropriate life stage for
ranges, light, air circulation, and moisture transplanting to field/garden
conditions
• When and how to deliver supplemental
• Physiological process of seed germination and fertilization
seedling development, and its relationship to
environmental conditions • How to manage pests and pathogens:
Monitoring, identification resources, and
• Optimal conditions for early stages of plant active management
growth up to transplanting stage, including the
hardening off process and movement of plants
through facilities

• The role, timing, and tools used in supplemental
fertilization

• Preventive and active pest and pathogen
management

Part 1 – 98  |  Unit 1.3  Introduction
Propagation/Greenhouse Management

Lecture 1: Seed Biology, Germination, &
Development—Environmental Conditions
& Cultural Requirements

Pre-Assessment Questions
1. What are the advantages of propagating annual vegetables in a greenhouse or similar

climate control structure compared to direct seeding crops?
2. What conditions must be met for a seed to successfully germinate and grow into a viable

seedling?
3. What are the key environmental conditions that facilitate germination and influence

seedling development of annual vegetables?
4. What are the characteristics of seedlings when ready for transplanting to the field or

garden? What actions may growers take to prepare seedlings for transplanting into the
garden or field?
5. What is the most effective way to manage/prevent the development of pest and diseases
in a propagation facility? Where would you seek information to identify pests or pathogens
and to find Organic Materials Review Institute- (OMRI-)/National Organic Program-certified
active control options if pest and or diseases should affect your seedlings?

A. Sexual Propagation
1. Definition: The intentional reproduction of a new generation of plants by the germination

and growth of seeds that were created in the previous generation through the fertilization
of a plant ovary via the union of male and female sex cells. Results in a genetically unique
plant generation.
For comparison, asexual propagation is the reproduction of plants by means of division,
cuttings, tissue culture, etc. This process occurs in nature, but is a primary method for
reproducing many ornamental cultivars and the vast majority of fruits, berries, and nuts.
Clonal or asexual propagation results in a new generation of plants genetically identical to
the parent or source plant, thus carrying forward all desirable/known characteristics in a
predictable manner.
2. Types of plants grown from seed
a) Annuals: Plants that germinate, grow vegetatively, flower, and produce seeds, thus

completing their entire life cycle within a single year. Sexual propagation (propagation
using seeds) is the only practical means of propagation for annuals.
b) Biennials: Plants that complete their entire life cycle within two years. Growth is
primarily vegetative in year one. In year two, growth is directed primarily toward
reproduction in response to vernalization: The process wherein plants are exposed
to decreasing day length and temperature followed by increasing day length and
temperature. This process occurs in temperate climates when plants go from one
growing season, through Winter and into the following Spring. Sexual propagation is
the only practical means of reproducing biennial crops.

Lecture 1: Seed Biology, Germination, & Development Unit 1.3  |  Part 1 – 99
Propagation/Greenhouse Management

c) Perennials: Plants that live more than two years. Once beyond their juvenile life phase,
perennials grow vegetatively, flower, and produce seeds every year. The life span of
perennials depends on the genetics of the species and the environmental conditions
in which the plants are growing. By definition, perennials can live three to thousands
of years, but lifespan within a particular species tends to vary. Perennials can be grown
from seed, although many are reproduced asexually/vegetatively to hasten maturity,
maintain genetic uniformity, and therefore retain desired morphological characteristics.

3. Open pollinated (OP) and hybrid seed (see also Appendix 1, Characteristics of Open-
Pollinated (OP) and Hybrid Seed)

a) Open-pollinated seed: Produced when a parent plant is fertilized by another member
of the same genetically stable population. Offspring bear traits or qualities that closely
resemble the parent population. These seeds may come from:

b) F1 Hybrid seeds: The product of cross pollination of two different, but homogeneous
inbred, stable lines, each of which contribute desirable characteristics to the subsequent
generation. Seeds saved from this next generation typically possess a highly
heterogeneous nature and will produce offspring unlike the hybrid parent population.

B. Seed Germination and Early Seedling Development
1. Necessary pre-conditions for seed germination
a) Viability: Seeds must contain living, healthy embryonic tissue capable of germination.
i. Viability depends upon the full development of the embryo and endosperm (nutrient

storage tissue) during the development of the seed
ii. Viability is also contingent upon maintaining the health of the embryo and

endosperm from seed maturation through seed sowing. Moisture within the seed,
nutrient reserves, and an embryo’s potential to germinate are finite, as determined by
the genetics of the species and by the environmental conditions during seed storage.
See Appendix 2, Seed Viability Chart, for typical lifespan of common vegetable seeds.
b) Many species also exhibit dormancy factors that inhibit or delay seed germination.
Dormant seed cannot germinate under what would otherwise be conditions favorable
for germination until dormancy factors have been overcome. Physical and chemical
dormancy are more common in native species and plants from more extreme
environments than in commonly grown vegetable and flower crops.
i. Physical dormancy (e.g., hard, thick seed coats): Can be broken by soaking, scarifying,
exposure to soil microorganisms. Methods are species specific. (See Resources
section for guides to propagation techniques.)
ii. Chemical dormancy: Growers replicate natural processes and environmental
conditions to break internal chemical/metabolic conditions preventing seed
germination (e.g., leaching, cold/moist stratification, fire scarification, etc.)
2. Environmental factors involved in germination are typically both atmospheric and edaphic
(soil related). Biotic factors, such as pests, pathogens, weeds, and microbes can also be
involved.
a) Temperature: For ungerminated seed, temperature is normally discussed in reference
to soil temperature. All seeds have minimum, maximum, and optimal soil temperature
ranges within which germination is possible (see Appendix 3, Soil Temperature
Conditions for Vegetable Seed Germination).
i. Minimum: Lowest temperature at which seeds can effectively germinate. As
compared to temperatures in the optimal range for a given species, days to
emergence will be long, percent germination will be low and rate of subsequent
growth will be slow when temperatures approach the minimum threshold for a given
species.

Part 1 – 100  |  Unit 1.3  Lecture 1: Seed Biology, Germination, & Development
Propagation/Greenhouse Management

ii. Maximum: Each species has an uppermost temperature at which germination
can occur. Above this threshold, injury or dormancy are often induced. Nearing
this threshold, percent of germination often declines and days to emergence may
increase.

iii. Optimal: Every species has on optimal temperature and corollary temperature range
in which the percent germination is highest and days to emergence is the lowest.
This is the target range to strive for when managing greenhouse facilities or sowing
seeds outdoors.

iv. In addition to optimal temperatures, some species either require or benefit from day-
night temperature fluctuation. Many small-seeded species, which best germinate
near the soil surface, benefit from the temperature fluctuation that normally occurs
at the soil surface. Germination may be inhibited in species requiring temperature
fluctuation if seeds are buried too deeply, as temperatures typically remain more
constant at depth.

b) Moisture: All seeds require moisture to initiate metabolic processes and support
germination. Seeds imbibe water from the soil pores in direct contact with the seed; as
this soil dries, moisture is replaced by capillary action from nearby soil pores, helping
facilitate germination. For most seeds, field soil or propagation media should be
maintained at or above 50%–75% of field capacity during the germination phase, and
have a firm, fine texture to provide good seed-to-soil contact.

c) Aeration: Soil/media must allow for gas exchange to and from the germinating embryo
i. Orexsypgireantio(0n2) dissolved into the soil media is required to facilitate embryonic
ii. aCwarabyofnrodmiotxhideese(CeOd2), a byproduct of respiration, must be able to dissipate and move
Note that good soil structure enhances gas exchange, whereby gases can move into

and out of the soil via the pore spaces between soil particles. Avoiding overwatering
and allowing for adequate infiltration of water and subsequent dry down between
irrigations also promote gas exchange. Excessive irrigation and/or poorly drained
soils can limit germination and development when oxygen is crowded out of the
pore spaces by persistent moisture.
d) Light can either induce or release dormancy, depending on the species. The effect of
light on sensitive species results either from light quality (wavelength) or photoperiod
(the duration of exposure.) Most cultivated crops express minimal or no sensitivity to
light during germination, in large part due to millennia of grower and breeder selection
for consistency and reliability of germination.
i. Most species germinate best under dark conditions by being slightly buried in the
soil medium, and in some cases (e.g., Phacelia, Allium, Phlox) germination may be
inhibited by light. Light inhibition is particularly common in desert species, where
germination in the presence of light would likely lead to desiccation and death due
to the normally dry conditions of the soil surface.
ii. Seeds of certain species (e.g., Lactuca, Begonia, Primula, Coleus) require exposure,
however brief, to light to induce germination. This is particularly common amongst
small-seeded species and is thought to be an evolutionary mechanism to prevent
germination when seed is buried deeply in the soil, where a germinating seed may
exhaust its resources before emerging above ground to begin photosynthesizing.
iii. The effect of light on germination should not be confused with necessity of light
for seedling development. All seedlings require sunlight for photosynthesis and
continued development.

3. Physiological steps in germination: A three-phase process leading to the emergence of
roots and above-ground growth

Lecture 1: Seed Biology, Germination, & Development Unit 1.3  |  Part 1 – 101
Propagation/Greenhouse Management

a) Phase 1: Imbibition. Rapid initial uptake of water by the dry seed, followed by a brief
but gradual continuation of water uptake. This softens and swells the seed coat and
occurs even in seeds that are no longer viable.

b) Phase 2: Interim or lag phase. Water uptake greatly reduced; internal physiological
processes begin. From the outside, little appears to be happening, but this is a very
active physiological and metabolic period within the seed.

i. Activation of mitochondria within cells of the seed: Supporting increased cellular
respiration and energy production

ii. Protein synthesis: Translation of stored RNA to fuel continued germination
iii. Metabolism and use of stored nutrient reserves to fuel development
iv. Enzyme production and synthesis, leading to the loosening of cell walls around the

embryo and root radicle, which will ease subsequent cell enlargement, division, and
elongation
c) Phase 3: Root radical emergence. Initially, root radicle emergence results from cell
enlargement, but this is rapidly followed by cell division and elongation as the root
radicle pushes into the surrounding soil media.
d) The processes internal to the seed and the below-ground emergence of the root radicle
define the process of germination. However, from a grower’s perspective, we typically
discuss germination in relation to when the plumule or embryonic shoot emerges
above the soil surface. It is at this point that we’re most aware of germination and must
shift our management practices, particularly to manage for relative wet to dry swings in
the soil to prevent the presence damping off organisms and other pathogens (see more
in Lecture 2, Managing Environmental Conditions—Using Greenhouses to Optimize
Seedling Production).

4. Early seedling development: Processes and shifting needs
a) Continued cell division-extension of root radical and root tip from base of embryo axis,

into the soil medium. Initial root development is unbranched and taproot-like.
b) Emergence of plumule or growing point of the shoot, from upper end of the embryo

axis. Initial, above-ground seedling development follows one of two patterns, either:
i. Epigeous germination: Ongoing elongation of the hypocotyl, raising the cotyledons

above ground where they provide stored nutrient transfer and initial photosynthesis,
until the emergence of the first set of true leaves. This normally occurs within 24
hours of above-ground emergence.
ii. Hypogeous germination: The hypocotyl does not continue to expand, and only the
epicotyl emerges above ground, soon followed by true leaves. The cotyledons deliver
nutrients for early development, but usually remain at or below the soil surface, and
photosynthesis comes exclusively from the true leaves.
c) Overall weight of seedling increases throughout developmental stages, while weight of
storage tissue decreases as stored nutrients are consumed by the growing seedling
d) Rate of respiration and volume of water uptake steadily increase with ongoing cell
division concurrent with the expansion of roots and above-ground shoots
e) As seedlings continue to develop through cell division and elongation, depending on
the root nature the species, a taproot, fibrous, or branched root system will develop,
with fine root hairs developing to increase the overall surface area available for
enhanced water and nutrient uptake
f ) Development of true leaves, roughly concurrent with development of branched root
system in most species, begins process of effective photosynthesis, helping to fuel
continued growth

Part 1 – 102  |  Unit 1.3  Lecture 1: Seed Biology, Germination, & Development
Propagation/Greenhouse Management

Illustration by José Miguel Mayo
Internal metaboliEcmperorgceenssceesoinf rmooottiroandicleemEexrpgaennscieonoforforootohtarairdsEipcliegeaonuds germination bebgeiEgnpinniignteogouunsfogledr,mainndatrioonotcsoynsttienmeuxepefsuax,lpncElyodamvntsyeidrslraeisgbpdelioend;nclaysenodfbtrruaenclehaevdersoaontdsysshtoeomt tip

C. Typical Life Cycle of Seedlings Grown in the Greenhouse: Timeline for Days to Seedling Maturity
1. The duration of seedling life cycle and growth rate depend on a number of factors
a) Photoperiod and the hours of light available to support growth. For most species longer

days translate into more rapid seedling growth, shorter days mean slower growth.
b) Temperatures within, above, or below the desirable range to stimulate or constrain

growth
c) Sufficient, consistent moisture to fuel growth. Too much or too little can inhibit normal

development.
d) Air circulation and gas exchange both above ground and in the root zone. Both are

critical to healthy seedling development and timely development, while too little
circulation or exchange invariably slows growth.
e) Nutrient availability, although note that excess nutrients may make for lush, weak
growth, vulnerable to pest, diseases, moisture, and temperature stress. Limited nutrient
supply will likely mean slow growth and poor performance. Appropriate nutrient supply
will fuel steady, uninterrupted growth and reduce vulnerabilities.
f ) Container type and cell size, with seedlings maturing as smaller transplants more rapidly
in smaller cells and more slowly as larger transplants in larger cells (see more at Lecture
4, Soil Media, Fertility, and Container Formats)

Lecture 1: Seed Biology, Germination, & Development Unit 1.3  |  Part 1 – 103
Propagation/Greenhouse Management

2. Producing seedlings ready for transplant can take as little as two weeks for fast-growing
crops such as lettuce and brassicas grown in small cells under optimal environmental
conditions, and up to ten weeks or more for slower-growing species such as peppers, and
alliums grown under less than perfect conditions or when producing larger transplants for
field production

The process of cycling plants from your most precise environmental control during
germination and early development, through seedling maturation and the process of
hardening off will be explained in greater detail in Lecture 2

D. Qualities/Characteristics of Seedlings Ready for Transplanting
1. Seedlings ready for transplant ideally should have:
a) A root system and root knit sufficient to hold together soil surrounding the roots
b) At least two sets of well-developed true leaves, true to color for the species
c) Cycled through the process of “hardening off,” whereby seedlings have been exposed to

outdoor conditions similar to their eventual in-ground growing environment for at least
several days, including full exposure to day-night temperature fluctuations to help build
carbohydrate reserves, and full exposure to the wind and sun to strengthen cell walls
and enhance tolerance to future the extremes in growing conditions

2. Holding: Maintaining seedling quality when transplanting is delayed
a) At times, transplanting may be delayed and it may not be possible to transplant

seedlings when they are at their optimal stage of development. This could occur:
i. When excessive rains prevent cultivating and preparing the soil
ii. When inadequate rain means it is too dry to prepare the soil without degrading soil

structure and you must wait for rain or pre-irrigate
iii. In cases of succession planting, when the ground for your new seedlings is still

occupied by a crop that has not yet matured
iv. When you are unable to prioritize new plantings due to other seasonal demands
b) There are several ways to keep your plants in good condition until you are ready to

transplant:
i. Know which crops tolerate holding and delays in planting and which do not. For

those that do not hold well, prioritize their planting whenever possible:
• Cucurbits, heading brassicas, bulbing onions, and peppers, for example, typically

do not respond well to holding
• Leeks, tomatoes, collards, and kale are all crops that can be held well, both

responding to holding strategies and rebounding well once transplanted
ii. Provide supplemental fertility to compensate for the nutrients that may no longer

be available in your soil mix. As seedlings use up available nutrients, growth will
invariably slow—supplemental fertility can address this issue.
iii. Move seedlings into a cooler location or microclimate to slow the rate of growth
iv. Move seedlings into partial shade to reduce photosynthesis and slow growth.
Note that plants may need to be hardened off again if they are held in shade for an
extended period in order to prepare them for garden and field conditions.

Part 1 – 104  |  Unit 1.3  Lecture 1: Seed Biology, Germination, & Development
Propagation/Greenhouse Management

Lecture 2: Managing Environmental
Conditions—Using Greenhouses to Optimize
Seedling Production

A. Optimizing Germination, Seedling Development, and Seedling Maturation
The principal role and function of greenhouse facilities is to modify or manage environmental

conditions to optimize plant health and development. Although greenhouse structures
serve many purposes, from producing transplants, to in-ground production of high value
crops, to early and late season extension in a range of climates, this lecture focuses on using
greenhouse facilities for seedling production.
1. Optimizing germination: Propagation structures, combined with the knowledge and

experience of the greenhouse grower, can be managed to create optimal environmental
conditions (e.g., temperature, air circulation, light, and soil medium moisture) that facilitate
rapid germination and early crop establishment
a) To promote rapid germination, temperatures must be maintained within the

appropriate range for chosen crops (see Appendix 3, Soil Temperature Conditions
for Vegetable Seed Germination). Temperatures below the optimal range will either
delay germination or promote erratic germination, and thus inconsistent seedling
age. Temperatures above the optimal range can induce thermo-dormancy in some
crops, such as lettuce and spinach, preventing or delaying germination. Temperatures
within the optimal range will promote rapid, uniform germination and consistent early
development.
b) Consistent air circulation is critical for crop health, both to provide adequate oxygen
for respiration and to mitigate against presence of fungal pathogens/“damping off”
organisms, which thrive with consistent soil moisture and stagnant air conditions
c) With recently sown seed and germinating seedlings, moisture delivery is typically
frequent and shallow. Consistent delivery, combined with high quality soil media,
prevents desiccation of imbibed seeds and emerging root radicals. However, a moderate
wet-to-dry swing in surface soil conditions, especially once crops have germinated, is
critical to prevent the presence and proliferation of damping off organisms.
i. Pythium, Rhizoctonia, Fusarium and Phytophthora, the primary genera of fungal

pathogens known as “damping off” organisms, can be controlled by managing
environmental and cultural conditions: Allowing for a wet-to-dry swing between
waterings, preventing stagnant air in the greenhouse, promoting consistent airflow,
and when necessary, managing for temperatures that limit pathogen proliferation
2. Promoting healthy early seedling development: Ongoing management of environmental
conditions (temperature, air circulation, and moisture delivery) is required as seedlings
develop, but with most species, seedlings’ physiological tolerance expands and precise
environmental control may be less necessary to maintain optimal development. When
greenhouse space is at a premium, young seedlings are typically moved to alternative
structures (from a greenhouse to a hoop house, for example) to make way for the next
generation of crops most dependent on precise environmental control.
a) Temperature management remains critical, especially when trying to extend seasonal
parameters. Growing in the protected/moderated environment of the greenhouse or
hoophouse will promote more rapid development than normally possible outdoors by
creating more favorable daytime conditions and minimizing nighttime chilling of crops
and soils, which will slow the resumption of growth the following day.

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Note: Optimal temperatures for germination and subsequent growth differ for some
crops (e.g., Brassicas) and thus germination might be optimized in a greenhouse,
while seedling growth might be best in a hoophouse or outdoors, depending on your
growing environment (contrast Appendix 3 with Appendix 5, Approximate Monthly
Temperatures for Best Growth and Quality of Vegetable Crops)

b) Maintaining good air circulation continues to be important in order to manage
temperatures, prevent diseases, and promote strong structural/cellular development

c) As seedlings develop, irrigation frequency typically decreases, but the depth/volume of
water delivered at each irrigation increases to support the expanding root system and
leaf canopy, and the increased transpiration rate. Reduced frequency and the resultant
wet/dry swing help prevent damping off damage and promote the beginnings of
drought tolerance as crops adapt to cope with short-term moisture limitations.

d) Sunlight is critical for developing seedlings to manufacture nutrients through
photosynthesis and to promote strong cellular growth and compact architecture.
While germination can take place in the absence of sunlight, for example in a growth
chamber (see below), healthy seedling development depends on adequate sunlight;
otherwise, crops will be weak and “leggy,” and thus less able to withstand the more
variable conditions encountered in the ground. In the hottest climates, full sun exposure
can cause tip burning and seedlings may require some shading, but eventually they will
need full exposure to prepare for in-ground life.

3. Managing seedling maturation and hardening off: Mature seedlings will typically have
a balance of root and shoot growth—at least two sets of true leaves and an ample root
system that holds together the root ball when removed from the growing container.
“Hardening off” is the final step in preparing seedlings for transplant and uninterrupted
growth. In the final 3–10 days in the greenhouse zone, seedlings should be outdoors
and exposed to conditions that most closely resemble their future home in the ground.
This acclimatization process reduces transplant shock, which can occur when seedlings
experience an abrupt transition from the protected environment of the greenhouse to the
less predictable conditions of a garden or field setting. During the hardening off process,
the following developments occur, which better enable plants to transition seamlessly to
their new homes in the ground:

a) Full exposure to natural day-night temperature fluctuation promotes a buildup of
carbohydrate reserves. When transplanted, reserves provide seedlings with a nutrient
buffer while they develop new roots to tap into soil resources.

b) Full exposure to stronger air circulation and prevailing wind patterns promotes cell
walls thickening, improving transplants’ ability to withstand the vagaries of the outdoor
environment

c) As plants approach seedling maturity, water is typically delivered less frequently, but in
greater volume

i. Reduced irrigation frequency supports the hardening off process and plants’
transition into the ground. Once in the field, seedlings normally must be able to
withstand longer periods between irrigations.

ii. Consistently providing water to the depth of the containers facilitates root
development and nutrient access across the full volume of soil available to seedlings,
thus maximizing development potential

d) Exposure to full sunlight, equivalent to future in-ground exposure, aids maturing
seedlings in cell development, cell wall strengthening and enhanced photosynthesis.
As with the benefits of the above-mentioned treatments, seedling exposure to full sun
conditions is another aid in reducing the potential for transplant shock.

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B. Passive and Active Environmental Management: A Brief Overview
The methods and tools used to manage environmental conditions in greenhouses normally

fall into one of two broad categories: Passive or active. Here we briefly describe these
categories; see Lecture 3, Greenhouse Heating, Cooling, Lighting, Irrigation, and Climate
Control Systems, for a more detailed discussion.

1. Passive methods of environmental control are part of the functional design of most
greenhouses and represent a low-tech approach that does not involve the ongoing use of
energy to regulate conditions. They include:

a) Heating by the capture of solar radiation as sunlight passes through the greenhouse
glazing and warms the interior air

b) Cooling via side and end wall vents that draw in cooler air from outside and ridge
vents at the top of the greenhouse that allow the heated air to be exhausted out of the
structure. Shade cloth or whitewash can also be used to help cool the greenhouse.

c) Air circulation via the venting system. As with cooling, exterior air enters the structure
through open side and end wall vents, and the air already in the greenhouse exits
primarily through ridge vents and vents placed high on end walls.

d) Irrigation can be delivered by hand or by overhead spray systems.
e) Lighting comes exclusively from sunlight. Light reduction via whitewashing and the use

of shade cloth is another form of passive management.
f ) Additional physical methods to heat and cool the greenhouse include the use of shade

cloth, white washing, and energy curtains

2. Active Methods

Active environmental controls use an external energy source to power heating, cooling,
venting, supplemental lighting, irrigation, and climate control systems. Active control
mechanisms are not a substitute for passive methods, but rather are complimentary tools
that allow growers to more precisely and predictably create desired conditions. Active
methods include:

a) Heating via conduction (direct contact with heating source), convection (via warm air
circulation), and radiant heat sources

b) Cooling via evaporative mechanisms (pad and fan systems), swamp coolers, and fog
systems

c) Air circulation via exhaust and horizontal airflow fans
d) Supplemental lighting, including incandescent, fluorescent, high intensity discharge,

and high pressure sodium lights
e) Automated irrigation systems, including overhead sprinklers
f ) Thermostats, stage controllers, and computer-directed environmental controls that

monitor and control various heating, cooling, circulation, lighting, and irrigation systems

C. Environmental Control in Different Types of Propagation Structures
1. Passive Solar Greenhouse: Good environmental control is possible in relatively low-

tech facilities, especially in milder climates where growers do not face extremely hot or
cold conditions. As described above, these greenhouses rely on passive techniques (see
also Supplement 1, Examples of Daily Warm- and Cool-Season Greenhouse Management
Practices in a Passive Solar Greenhouse).
a) Trap solar radiation to warm the air and thus the crops
b) Cooled through the use of venting systems: Combination of end wall vents, roll up/down

sides, and ridge vents, to draw in cooler external air, and exhaust warmer internal air

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c) Air circulated by manual control of inlet and outlet venting; complements the heating
and cooling capacity of passive solar design

d) Moisture regulation/delivery managed by the grower through manual/hand delivery,
semi-automated, or automated delivery systems

e) Microclimatic heating may be possible; offers additional environmental control when
power is available to supply the system, but this goes beyond the purely passive

2. Enclosed (semi) Automated Greenhouses: Precise environmental control achievable via
active mechanisms:

a) Characterized by ability to fully close growing environment, regulate temperatures/air
circulation through passive and active venting and fan-driven air movement, heating/
cooling by fans, furnaces, swamp coolers, etc. (see Lecture 3 for details)

b) The interplay of environmental conditions and sophistication of active management
tools dictate the precision of environmental control: More precise control comes with
more responsive systems and lesser extremes in conditions to be regulated

c) Trapped solar radiation works in concert with active heating mechanisms to create
desired warmth

d) Cooling via passive venting systems works in concert with active cooling mechanisms to
create desired temperatures

e) Microclimatic heating in root zone via hot water pipes or electric cables is often used to
optimize conditions and speed the rate of plant growth

f ) Automated or manually controlled sprinkler systems are the norm in more actively
managed and infrastructure-intensive greenhouses, but spot watering by hand remains
critical to optimize plant health

3. Open Hoop Houses/Quonset Huts: Can partially modify environmental conditions and
improve plant health, especially in milder climates

a) Temperature modification: Umbrella-like coverage creates slightly warmer day and
night conditions, which favors more rapid development than possible outdoors

b) Provide some buffering against effects of wind, though air circulation may be limited
by how structure is located relative to prevailing winds, nearby windbreaks, and other
structures, unless the hoop house is outfitted with roll up or roll down sides and end
wall venting

c) Grower controls moisture regulation, delivering necessary irrigation through same
means as in greenhouses

d) Can be used as an intermediate step between greenhouse and outdoors: Greater
exposure of plants to wind and day-night temperature fluctuations offers a gradual step
in the hardening off process, especially when the favorable conditions created in the
greenhouse are dramatically different than prevailing outdoor conditions

4. Germination Chambers: Small-scale, self-contained facilities that provide optimal control
over temperature and humidity to facilitate rapid, high-percentage germination

a) Whether pre-assembled or home made, chambers are comprised of a water-holding
pan, a submersible heat source with variable temperature control, a water supply,
insulated walls, suitable shelving to hold propagation trays, and doors large enough to
easily move containers in and out of the chamber. Units usually hold between 24–48
propagation trays but can be designed larger or smaller to meet needs.

b) Together, these elements create an energy efficient, very consistent environment for
germination where humidity and temperature can be optimized to greatly improve and
speed germination

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c) Rapid germination in chamber’s compact space can save growers significant heating or
cooling costs, depending on the season

d) Higher percent germination can reduce seed costs
e) Must be regularly monitored: Once seedlings germinate, propagation trays must

immediately be removed from the darkness of the chamber and moved to a sunny
location to facilitate normal cell development and photosynthesis
5. Cold Frames: Small-scale, low-tech structures used to modify environmental conditions.
Similar to passive solar greenhouses and hoop houses that do not contain any
supplemental infrastructure.
a) Simple structures, normally placed directly on the ground, consisting of four low walls
(insulated in colder climates) and a sloping, hinged roof that allows in sunlight for
warmth and photosynthesis. Roof can be opened to facilitate cooling and air circulation.
b) Often built of recycled materials, such as wood and rigid insulation board for siding and
old windowpanes or clear acrylic panels salvaged from local resource recovery facilities
for the roof
c) Sunlight can quickly heat internal air and enclosed air mass will provide some buffer
against cold nighttime temperatures; due to small size, cold frames provide limited
buffering capacity and are prone to rapid temperature shifts as external temperatures
change
d) Cooling and air circulation are achieved through opening the roof. Relying on this
passive exchange, while effective, can be problematic if the cold frame is left closed for
too long during warm conditions.
e) Irrigation is usually done by hand and can provide a secondary form of cooling through
evaporation
f ) Through greater venting or leaving a cold frame open overnight, increased air flow and
day-night temperature fluctuation can help initiate hardening off
6. Outdoor Benches: In most growing environments, seedling maturation or hardening off
is completed by placing seedlings outdoors on benches, exposing plants to conditions
that closely approximate the in-ground environment they are moving toward. As detailed
above, full exposure to sunlight, wind, and temperature swings stimulates carbohydrate
reserve buildup and strengthens cell walls so that plants can withstand the vagaries of the
in-field environment.
7. Shade Structures: While most annual vegetable seedlings require full sun to optimize
growth, shade cloth may be needed in hotter climates to prevent soil media from drying
out so rapidly that the grower must constantly devote time and water to keep young
seedlings healthy

D. Irrigation Management and Delivery
1. Greenhouse irrigation concepts and terminology are similar to those used in the garden

and field setting (see Unit 1.5, Irrigation–Principles and Practices). However, because of the
small soil volumes plants are growing in and because of the design of propagation and
nursery containers, water behavior in greenhouse containers and consequent practices can
be quite different.
a) Saturation: As with field soils, saturation in containers comes at the point when

irrigation water fills all of the pore space in the soil medium, but in high quality mixes,
this is only a very temporary state and excess moisture quickly drains from the mix
b) Container Capacity: Similar to Field Capacity, container capacity is when excess water
has drained, air has returned to part of the pore space, and maximum water is held in
the pore spaces against the forces of gravity

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c) Percent Container Capacity describes the relative availability of water in the mix as water
is lost to uptake by the plant roots and evaporation

d) Perched Water Table describes the water that is held at the bottom of flat-bottomed
containers. This condition may be detrimental to plant health if the soil mix does not
contain an adequate amount of coarse materials to promote good aeration throughout
the root zone.

e) Percent Surface Dry Down is another important concept in the greenhouse setting, and
applies specifically to the germination phase of seedling production when frequent
but small quantities of water must be delivered to facilitate germination and prevent
desiccation of newly emerging roots

i. For the vast majority of seed-grown crops, a small quantity of water should be re-
applied when somewhere between 30–50% of the visible soil surface has dried down

ii. For larger-seeded crops such as sunflowers and members of the cucurbit family,
growers typically allow 100% of the surface soil to dry down before re-applying
moisture

f ) Post germination: Greenhouse growers deliver water in direct response to crops needs,
the age and stage of development of their crops, and the immediate and anticipated
environmental conditions that crops are experiencing

E. Pests and Pathogens in Propagation Facilities

1. Management program begins prior to propagation with preventive measures, identifying
and eliminating the possibility of contamination

a) The propagation facilities: Greenhouse structures, greenhouse floors, pots, flats, hand
tools, hoses, benches, etc. can all harbor plant pathogens. Good sanitation programs
should include periodic cleaning or disinfecting of all materials and facilities.

b) Propagation media can be another source of contamination, especially for soil borne
bacteria/fungi and weed seeds (see Lecture 4, Soil Media, Fertility, and Container
Formats). To minimize this risk, growers can:

i. Use biologically active, disease-suppressing media based on high quality composts,
and/or inoculated with beneficial fungi or mycorrhizae

ii. Use sterile, soilless media that comes from sterile sources, lacks biological potential,
or has been previously treated to eliminate pathogens

iii. Use heat/steam and solar pasteurization methods to sterilize media, a costly
but effective method that will eliminate pathogens and beneficial organisms
simultaneously

c) Seed/plant stock can also be a source of contamination. The grower can protect against
this potential by:

i. Using seed/propagule material that comes from reliable sources and is certified to be
pest and disease free

ii. Using seed pre-treatment techniques such as hot water baths to kill fungi and other
pathogens

d) Exclude pests from growing environment
i. Screen at all points of entry into the greenhouse, including vents, fans, and doorways
ii. Use floating row covers over cell trays to keep flying insect pests off of emerging

crops
iii. Use physical barriers such as water basins or sticky resins on table legs to prevent

ants and other crawling insects from having access to young crops

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2. Good cultural practices are a critical component in the management/prevention of pest/
disease challenges

a) Select pest- and disease-resistant varieties and avoid crops vulnerable to known
potential problems. Check with local growers and extension agents for issues common
in your area for the crops you grow.

b) Grow crops at appropriate seasonal junctures, where environmental conditions
naturally facilitate healthy, vigorous, pest- and disease-resistant growth

c) Manage environmental conditions to mitigate against the presence of pests/disease
and promote vigorous, uninterrupted growth. This includes the management of:

i. Temperature: Especially important in the prevention of damping off organisms,
which thrive when soils are constantly moist and temperatures are steadily in the
68ºF to 86ºF range. While this range is both ideal for damping off organisms and
for the growth of many common crops, damping off damage can be prevented by
using high quality soil media, making sure the soil goes through adequate wet to dry
swings, and sacrificing optimal temperatures when cooling will control damping off
fungi.

ii. Moisture: The quantity and frequency of moisture delivery is critical to healthy
seedling development. Constantly wet soil deprives roots of necessary oxygen, limits
the mobilization of organic nutrients in the soil mix, and can create conditions that
favor damping off and root rotting fungi. Excess irrigation can also lead to nutrient
leaching from the soil media, depriving plants of valuable resources and potentially
compromising local surface or groundwater quality (see Supplement 2, Conserving
Water and Protecting Water Quality).

iii. Air circulation: Circulation or oxygen exchange within the greenhouse, as previously
highlighted, helps regulate greenhouse temperatures, is critical in promoting strong
cells and healthy growth, and prevents pathogen buildup

iv. Fertility: In concert with other cultural practices, adequate but not excessive soil
fertility promotes healthy, uninterrupted growth. Excess fertility can lead to lush,
rangy growth and attract aphids and other insects that feed on nitrogen rich crops
(see Appendix 6, Sample Soil Mix Recipes, for examples of mixes with appropriate
fertility).

3. Management also includes monitoring and early detection of pest/disease problems to
minimize crop loss and need for intervention

a) Monitor at regular frequency: Make close observations to look for early signs of disease
and pest presence; use yellow or blue sticky traps to sample for and or control flying
insects such as shore flies and fungus gnats

b) Use pest and disease identification tools such as the books and websites listed in
the Resources section of this unit (see also Unit 1.8, Managing Arthropod Pests and
Unit 1.9, Managing Plant Pathogens). These resources can help with understanding
life cycles, seasonal and environmental conditions that favor pests and pathogens,
cultural strategies that can prevent or minimize problems, and in some cases, suggest
organically approved inputs to use when intervention is necessary.

c) Establish clear tolerance thresholds to initiate control actions, when shifts in cultural
practices and environmental management does not provide adequate controls

d) Rogue (cull), or quarantine infected crops to prevent the spread of problems to nearby
crops susceptible to the same pests or diseases. Roguing requires sacrificing some
for the good of the whole. Quarantining allows treatment strategies to be applied
selectively and in isolation from other susceptible crops, thus reducing the likelihood of
more widespread outbreaks.

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e) As a last resort, use organically acceptable chemical controls, or biological control
agents that specifically and selectively target the pest or disease problem you are trying
to manage. Following as many as possible of the above strategies and intervening early
can greatly reduce losses and increase the efficacy of the inputs organic growers have at
their disposal.

f ) While most greenhouse pests and pathogens are common across the country because
of the similarity of environmental conditions created in greenhouses, speak with local
growers, cooperative extension agents, and IPM practitioners to find out what problems
to anticipate in your region, which crops may be most vulnerable, the potential severity
of particular pests and pathogens, and the times of year to be especially vigilant



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Lecture 3: Greenhouse Heating, Cooling,
Lighting, Irrigation, & Climate Control Systems

A. Passive and Active Environmental Management
As discussed briefly in Lecture 2, passive and active methods are the two general categories of

techniques used to manage environmental conditions in greenhouses
1. Passive methods
Passive methods are part of the functional design of most greenhouse structures and

represent a low-tech approach that does not involve the ongoing use of energy to regulate
conditions
a) Heating is achieved by the natural capture or trapping of solar radiation as sunlight

passes through the greenhouse glazing and warms the air within the structure. The
extent to which you can heat or even overheat a greenhouse solely through trapped
solar radiation depends on your regional climate, how the greenhouse is situated
relative to other buildings, trees, etc., and the aspect or slope orientation of the site.
b) Double Wall Glazing: Double wall polycarbonate roofing and double layers of
polyethylene film held aloft by fans can provide a measure of insulation and a buffer
against rapid temperature swings
c) Internal Curtains: Retractable by day to maximize light infiltration and deployed at
night, modern curtains reflect heat back into the greenhouse and further buffer crops
against nighttime low temperatures
d) Cooling occurs principally through the use of side and end wall vents that draw in
cooler air from outside of the greenhouse, and by vents located along the ridgeline
that allow the heated air to escape. The capacity to cool greenhouses solely by passive
means is partly a function of structural design, but is largely determined by local climate
conditions, exposure to prevailing winds, and the intensity of sunlight heating the
house. When it is 90ºF outside, an unvented greenhouse can easily rise to 130ºF. Even
with early, preventive venting, it can be difficult to keep interior temperatures below
100ºF.
e) Some cooling can be achieved by covering structures with shade cloth or whitewashing
to reflect solar radiation, but the efficacy of these methods is again dictated by
local climate. This also reduces light transmission, which can negatively impact crop
performance, slowing growth rates, creating weaker, leggy plants and softer, more
tender tissue.
f ) Air circulation occurs exclusively via the design, functionality, and deployment of the
venting system. As with cooling, exterior air enters the structure through side and end
wall vents; the air already in the greenhouse exits primarily via ridge vents and vents
placed high on end walls. Despite a lack of active mechanisms (fans, blowers, etc.) to
exchange air, the side, end wall, and ridge vents sized appropriately for the structure,
can effectively promote air circulation and exchange. This can be a vital tool in limiting
the presence of disease pathogens, as discussed in Lecture 2.
g) Irrigation in passive structures can be delivered by hand or by overhead spray systems.
The greenhouse manager must make ongoing, real time decisions to determine when
and how much water to apply to what crops.
h) Lighting in passive structures comes exclusively from the sun and is dictated by your
regional climate, how the greenhouse is situated relative to other buildings, trees, etc.,
and the aspect or slope orientation of the site. Light reduction via whitewashing and
shade cloth is another form of passive management.

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2. Active methods
Active methods are also part of the functional design of greenhouse structures, but use

an external energy source to power mechanisms that enhance the greenhouse grower’s
ability to more precisely manage temperatures, air circulation, and water delivery
a) Active environmental controls inherently drive up construction costs because additional

mechanisms must be purchased and installed. In many climates, and for some crops,
these tools are critical to achieve appropriate environmental control. Over time,
increased labor efficiency and improved crop performance can make up for upfront
costs.
b) Active control mechanisms are not a substitute for passive methods, but rather, are
complimentary tools that allow growers to more precisely and predictably create
desired conditions
c) Design considerations are based on how hot or cold your climate gets, combined
with the desired temperature ranges for the crops you grow. These will determine
the importance of and type of heating and cooling infrastructure to incorporate into
greenhouse design.

B. Principle Heating and Cooling Mechanisms
1. Active/Supplemental Heating can be delivered to the greenhouse environment several

ways:
a) Conduction: Conductive heating occurs when growing containers are in direct contact

with the heat source. Heat is transferred from the source to the soil media and then to
the plant roots and canopy. Electric heat mats, benchtop hot water piping, and radiant
floors are all examples of conductive heating.
b) Convection: Convective heating occurs when warmed air is moved around plants via
fans or other means of air circulation, transferring warmth to the soil and crop. Unit
heaters and perimeter fin/pipe systems, combined with fans, are examples of convective
heating.
c) Radiation: Radiant heating occurs by way of infrared waves transferring heat energy to
the crops. This takes place when crops are placed close to the heat source, such as when
growers install hot water piping under benches, and for the crops closest to perimeter
fin/pipe systems. Most mechanical heat sources actually deliver a combination of
radiant and convective heat.
3. Heating mechanisms
a) Unit heaters, functioning by convection, are normally suspended from the upper
structure of the greenhouse, and can be gas or electric powered, depending on
available energy sources and costs. A unit heater consists of a heating element/
fuel combustion chamber and fans to move the heat from the source through the
greenhouse. In larger greenhouses and in colder climates, growers use multiple unit
heaters and/or perforated duct systems to more uniformly distribute heat.
b) Hot water systems, such as the perimeter fin/pipe, and under-bench hot water piping,
heat the air of the greenhouse, which then radiates and is moved by convection to the
containers/soil and crops. These systems can be powered by natural gas, propane, oil,
wood waste, geothermal, or solar batch collectors, depending on resource availability
and costs.

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c) Micro-climate heating: In the form of bottom heat, whether electric mats or hot water
tubing directly on the bench tops, can be the most energy efficient because the grower
does not necessarily strive to heat the air of the entire greenhouse, but rather the soil/
root zone and by extension the leaf canopy through conduction. Heat mats are normally
electric, must be plugged in to a power source and generally are used for smaller-scale
operations. Closed loop, bottom heat hot water tubing, such as the Biotherm system,
can be powered by electricity, gas, or be connected to a solar hot water system to
efficiently heat the root zone. This type of system can be particularly useful for heat-
loving crops such as Solanums and Cucurbits.

4. Cooling mechanisms

Cooling mechanisms are required for summer greenhouse production in all but the
mildest environments. In virtually all other growing environments, trapped solar radiation
can create an environment too hot for most seedlings. The importance of active cooling
mechanisms cannot be overstated unless you are only producing heat-loving crops.

Depending on the crops you grow, the size of your facilities, and the nature of your climate,
different cooling mechanisms may be available to you

a) Evaporative Cooling
i. Fan and pad systems combined with exhaust fans are commonly used in actively

managed commercial greenhouses
• Fan and pad systems are electrically powered and are made up of corrugated

cellulose pads housed on one wall of the greenhouse. A water reservoir and pump
system saturates the pads, and a fan evaporates the water in the saturated pads.
Air coming into the greenhouse is cooled via the heat energy absorbed as the
water evaporates.
• Fan and pad systems, combined with exhaust fans, must be appropriately sized
for the greenhouse structure, and the environmental conditions that need
modification
• These systems work most efficiently in drier climates; in high humidity
environments, systems should be over engineered by approximately 20% to
compensate for the inefficiency of evaporative cooling in already water-saturated
air
• While highly effective, fan and pad systems can be costly to operate during peak
electricity rate periods, which coincide with the times/conditions when the
systems are most needed
• Typical fan and pad systems operate at about 85% efficiency and have a
temperature differential of as much as 7–10ºF because cooling is centralized at the
fan and pad, and depends on the fans and exhaust system for distribution across
the structure
b) Swamp coolers work on the same principle as fan and pad systems, but are usually
installed in smaller structures, often without active exhaust fans. Instead, the
evaporatively cooled air is moved across the structure by strong fans within the swamp
cooler; warmed air exits the structure passively through ridge and end wall venting.
c) Fog systems also work on the same evaporative cooling principles, but distribute fog
across the entire greenhouse through careful placement of atomizing nozzles
i. Results in nearly 100% cooling efficiency, with temperature differentials at no more
than 1ºF
ii. Can be used in greenhouses with only natural ventilation and/or mechanical
ventilation
iii. Operate under high pressure, with water forced through very fine-aperture fog
nozzles. Clean water and regular maintenance are required to keep the systems
operating properly.

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5. Physical methods for heating and cooling

Additional heating efficiency and cooling can be achieved through physical/mechanical
means such as the use of shade cloth, white washing, and energy curtains

a) Shade cloth can be purchased in a range of shade densities and can be installed on the
interior or exterior of the greenhouse. Shade cloth reduces light intensity and thus heat
from solar radiation. Relatively inexpensive materials can provide years of service and
reduced cooling costs. However, excess shade for sun-loving crops can lead to weak,
leggy growth that will be more vulnerable to pests and to damage by winds and frosts
when transplanted.

b) White washing, a traditional method of reducing light intensity and temperatures,
reflects solar energy away from the greenhouse, thus reducing interior heat and the
need for cooling. Very inexpensive, but must be removed in the winter months to
improve solar heating potential and reapplied the following season. As with shade
cloth, reduced light levels can lead to weak, leggy growth in some crops.

c) Energy curtains, are the most expensive but most versatile of these physical/mechanical
tools. Energy curtains are retractable coverings, made of either plastics or aluminized
polyesters. When deployed, they trap an insulating layer of air between the crops and
the greenhouse roofing; they reduce the total volume of air that must be heated to
satisfy crop requirements and the metallic fabrics heat energy back into the crop zone.
Additionally, on hot, sunny days, they can be deployed to act as a shade barrier, thus
reducing greenhouse temperatures and the need for additional cooling. Energy curtains
can cost several dollars per square foot to purchase and install, but with every rising
energy costs, the improved energy efficiency they provide can be recouped in as little as
two to three years.

C. Air Circulation
1. Active air circulation moves cooler exterior air into the greenhouse to keep temperatures

down. Simultaneously, air movement induces evaporative cooling when plants respire and
when humidity in the air evaporates and absorbs local heat energy.
a) Exhaust fans should be sized according to your climate, crop needs, and the size of the

structure requiring ventilation
i. Propeller-type exhaust fans should be large enough to exchange the entire interior

air volume in just one minute. While this might sound extreme, this is the standard
for active ventilation and can normally prevent interior air from being more than 10ºF
above exterior temperatures.
ii. Inlet vents and pad and fan type cooling systems are normally positioned on the
windward side of the greenhouse to maximize the potential for the movement of
exterior air into the greenhouse
iii. Exhaust fans are normally positioned on the leeward side of the greenhouse to
maximize their potential to move heated air out of the structure
b) Horizontal Air Flow (HAF) Fans, are usually 1-3” in diameter and are attached to the
greenhouse structure at the height of the top of the side walls
i. HAF fans serve to provide consistent air circulation even when the greenhouse is
tightly closed to retain internal heat
ii. HAF fans help reduce excess humidity in the greenhouse, especially when
condensation builds up over night, helping reduce the incidence of fungal issues
iii. HAF fans are normally suspended no more than 50-80” apart and work best when
positioned so that fans on opposite sides of the greenhouse are blowing air in
opposite directions, thus creating a circular movement pattern
iv. HAF fans add little extra air movement beyond what passive and active air circulation
systems provide and are not normally powered on when venting and fans are in use

Part 1 – 116  |  Unit 1.3  Lecture 3: Greenhouse Climate Control Systems
Propagation/Greenhouse Management

D. Supplemental Lighting
Lighting systems that supplement available sunlight can increase crop productivity and

quality
1. Can improve plant growth in low light and short day length conditions, e.g., during winter

in northern climates
2. Can manipulate photoperiod, and bring day length-sensitive crops to bloom out of their

normal cycle and thus have crops such as sunflowers blooming year round
3. Benefits must be weighed against the cost of purchasing and installing supplemental

lighting, as well as ongoing energy costs. Careful Return on Investment (ROI) calculations
should be made prior to purchasing any supplemental lighting to see if the initial expense
and ongoing costs can by justified by yields.
4. Incandescent and fluorescent lighting are the least expensive options but are only effective
in impacting day length sensitivity, and will not improve quality of growth
5. High Intensity Discharge (HID) and High Pressure Sodium (HPS) lighting units are required
if growers need to increase available light to improve plant growth. These are more
expensive to purchase and operate. If you are growing photoperiod-sensitive crops in low
light and short day length regions, then HID and HPS lighting can be used both to impact
day length and the quality of crop growth.

E. Irrigation Systems
1. Manual irrigation
Hand delivery requires the lowest amount of capital investment. One only needs a water

source, faucets, hoses, and tools such as a Fogg-It nozzle, the “rose on a hose,” or a wand
and water breaker combination to deliver water across the seedling life cycle. However,
relying exclusively on hand watering is very labor intensive and can lead to uneven plant
performance unless water is being delivered by a highly skilled irrigator.
2. Overhead delivery via semi-automated and automated sprinkler systems
A well designed sprinkler system can uniformly deliver water to an entire crop with very
little time/labor required
a) In semi-automated systems, typically the grower must assess plant/soil needs and then

determine when and how much water to apply. However, using mechanical timers
to semi-automate the system, delivery and shut off are provided by the timer and
overhead sprinkler system.
b) In fully automated systems, environmental sensors and computer-driven programming
are synchronized to respond to current environmental conditions and the needs of
developing seedlings. While much more costly to set up, well-designed automated
systems typically have a rapid return on investment, due to improved crop quality and
huge savings in labor.
c) Because of the “edge effects” of increased sun exposure and air circulation, plants at
the edges of benches and blocks will normally dry out faster that those in the interior,
so even automated and semi-automated systems usually require some hand watering
follow up. Even with this limitation, the labor savings such systems offer is immense and
can pay for the cost of investment in a single season.

Lecture 3: Greenhouse Climate Control Systems Unit 1.3  |  Part 1 – 117
Propagation/Greenhouse Management

F. Automated and Semi-Automated Climate Control Infrastructure
1. Thermostats are the least expensive and unfortunately least accurate environmental

management tools available for automation
a) Thermostats are positioned in the greenhouse to turn heating and cooling equipment

on at pre-determined temperature thresholds, based on your climate and crop needs
b) Older thermostats, while convenient, are notoriously inaccurate and may not give

the precise control desired. Additionally, separate thermostats are required to control
heating and cooling equipment.
c) Modern thermostats, while more expensive, offer more accurate control by using digital
or electronic technology to monitor temperatures and operate environmental control
equipment

2. Stage controllers offer dramatic improvement in precision of environmental control by
linking the operation of heating and cooling devices, air circulation mechanisms, and even
the deployment of energy curtains and shade cloth in the higher-end models

a) Stage controllers typically provide one or two set points to activate the heating
mechanisms in your greenhouse and three, four, or more stages of activation of the
cooling mechanisms

i. For example, as the greenhouse heats beyond a given threshold, at stage one vents
will open

ii. With continued heating, vents and fans will operate
iii. And with further heating, the pad and fan cooling system will be activated to

maintain the desired temperature
b) Stage controllers are only limited by the range of set points that activate your heating

and cooling mechanisms; higher-end models may also offer a data recording feature

3. Computer directed environmental controls offer the maximum level of precision in the
total environmental control of the greenhouse

a) Computer zone controllers, with or with without a PC, links all aspects of environmental
control—temperature, air circulation, water delivery, and lighting—through a single
device, offering a high degree of flexibility and the ability to customize the system

b) Integrated computer systems, using a PC, also provide maximum control of all aspects
of environmental conditions, with the added advantage of being able to control
multiple zones or separate structures from a single device. The most sophisticated
systems offer remote access through smart phones, tablets, and laptops, as well as the
ability to receive alarm warnings whenever conditions are out of the desired range or
components are malfunctioning.

Part 1 – 118  |  Unit 1.3  Lecture 3: Greenhouse Climate Control Systems
Propagation/Greenhouse Management

Lecture 4: Soil Media, Fertility, & Container
Formats

A. Soil Media and Plant Propagation

1. Role of propagation media

a) Whether purchased or made on farm, soil mixes for propagation and seedling
production are designed to provide an idealized growing environment by:

i. Providing a readily available nutrient supply to support steady, healthy plant growth

ii. Holding/retaining adequate moisture to meet plant needs without the need for
constant watering

iii. Allowing excess water to drain rapidly from the media. This prevents or limits the
presence of fungal pathogens and thus allows for proper aeration in the pore space
to promote healthy root development.

iv. Providing an environment for root anchorage and development

v. Being free of pathogens and weed seeds, which could compromise crop growth

b) Nutrients are primarily supplied in organic soil mixes by:

i. Compost: Source of moderate quantities of NPK, and micronutrients

ii. Soil: Field-based soils can provide NPK and micronutrients in small quantities

iii. Organically derived amendments and byproducts: Such as blood meal (13-0-0),
bone meal (4-14-0), cottonseed meal (5-2-1), feathermeal (12-0-0), fish meal (9-3-0),
soybean meal (7-2-1)

iv. Mineral amendments: Such as dolomite (Ca, Mg), greensand (K), rock dusts (Ca, Mg,
micronutrients), sulphate of potash (K, S), soft rock phosphate (P, Ca, micronutrients)

c) Moisture retention in soil media is achieved through the use of:

i. Composts

ii. Peat moss

iii. Coco Peat/Coir Fiber

iv. Vermiculite

v. Leaf mold

vi. To a lesser extent, moisture retention also provided by soil, sand, perlite

d) Adequate drainage in soil mixes is primarily provided by:

i. Coarse sand

ii. Perlite

iii. To a lesser extent, drainage is also provided by compost, vermiculite, peat moss, coco
peat, leaf mold (partially decomposed leaf litter), and partially decomposed wood
byproducts

e) Growing media must also provide aeration, allowing soil pore spaces to exchange O2
and CO2. This is accomplished through the use of:

i. Perlite

ii. Sand

iii. Vermiculite

iv. Leaf mold

v. To a lesser extent by peat, coir fiber, and coarse composts

f ) Soil media should be pathogen-free and by the nature of its composition and careful
cultural practices, should not be conducive to the development of pathogens

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B. Properties and Considerations of Principle Soil Media Ingredients

1. Composts
a) Can be an excellent source of short- and long-term nutrient availability, provide

moisture-holding capacity, are a source of bulk density, and provide some degree of
drainage and aeration
b) Can be produced on farm, are a way to use animal residues and recycle on-farm
nutrients
c) Can be a source of beneficial bacteria and fungi that promote plant health
d) Can also be the source of weed seeds and pathogens if not from a well-managed, high
quality source
e) Similarly, if not made from nutrient-rich sources or if too old, they can be a poor source
of nutrients

2. Field and garden soils
a) Assuming they are well managed sources, can be a decent source of macro and micro

nutrients
b) Can be a source of beneficial bacteria and fungi
c) Can provide valuable bulk density but at the same time contribute considerable weight

to propagation mixes
d) If used in too high a proportion, can create a poorly aerated and poorly draining

growing environment
e) Can be the source of weed seeds and pathogens if not from a well-managed, high

quality site, and can lead to the spread of weed and pathogens as soils are moved from
field to greenhouse to new fields

3. Coarse sand
a) Provides excellent drainage and aeration for soil mixes
b) Provides valuable bulk density but at the same time contributes considerable weight to

propagation mixes and is not suitable for use in polystyrene (Speedling type) containers
because sand readily scars the containers, creating sites that roots will cling to or that
can harbor pathogens
c) Although not a renewable resource, it is abundant around the world and thus does not
create long- distance transportation impacts

4. Perlite

Of volcanic origin, perlite is a mined mineral, ground, graded, and heated in kilns to 1600ºF,
which causes microscopic quantities of water in the ore to turn into a to gas. This in turn
causes the raw perlite to expand, popcorn style, to 4–20 times its original size.

a) An excellent source of drainage and aeration in soil mixes, while also being very light
weight and easy to handle

b) Can retain 2–3 times its weight in water
c) Is sterile when first removed from its packaging and is therefore not a source of weed

seeds or pathogens, and normally has a pH of 7.0
d) Greece, the United States, especially NM, UT and OR, along with China are the biggest

producers of perlite
e) Production is very energy intensive, from mining, to expansion of the raw ore, to

transport from remote locations to market
f ) Alternatives to perlite include sand, pumice, rice hulls, processed corncob waste, and

composted grape seed

Part 1 – 120  |  Unit 1.3  Lecture 4: Soil Media, Fertility, & Container Formats
Propagation/Greenhouse Management

5. Vermiculite

A micaceous mineral, vermiculite is mined and then processed in kilns heated to 1000ºF.
While in the kilns, microscopic water molecules trapped in the ore are vaporized, which in
turn causes the ore to exfoliate, accordion style, into a material that has a huge surface to
volume ratio.

a) Outstanding ability to hold water, at least four times its own weight

b) High cation exchange capacity (CEC) and especially effective at holding on to K, Mg, Ca,
and P

c) By virtue of its size and shape, provides good drainage and aeration, while also being
lightweight and easy to handle

d) Is sterile when first removed from its packaging and is therefore not a source of weed
seeds or pathogens, and has a pH of 7.0

e) Produced domestically in South Carolina and Virginia, imported from South Africa,
Brazil, China, and several other sources

f ) Alternatives to vermiculite include partially composted cotton gin waste, ground pine
and fir bark, sand, and leaf mold

6. Peat moss

Derived from wetland bogs in many countries in the far North, consists of the remains
of partially decomposed sphagnum moss, and allied plants, held in a state of very slow
decomposition because of the water-saturated, anaerobic environment in the depths of
the bogs

a) An outstanding source for water retention, holding 4–6 times its weight in water, while
at the same time providing for good drainage and aeration

b) Brings high CEC potential to mixes, and has a pH of approximately 4.5

c) There is debate as to the sustainability of peat mining practices. Also, peat bogs are the
adwdiosdrrulidnpg’stiltoaonrggceraesuetsnceahdrobbuoysneerxgetaprsaoecsstiiteoovnreierneslaeafantesdertssrihatepusgmaeroeqruereaCsnOttoi2triteehdsa.onfeCvOen2 intrtooptihcael rainforests. The
atmosphere,

d) Alternatives to peat moss include coco peat, partially composted wood waste,
mushroom compost, locally harvested leaf mold, and perhaps in the future, dairy waste
fiber sourced from anaerobic digesters

7. Coco Peat/Coir Fiber

A byproduct of the coconut industry, coconut husks/fibers were once disposed of, but now
have become a significant input in the horticulture industry, often used in place of peat
moss in nursery and greenhouse operations

a) Has outstanding ability to retain water, roughly six times its own weight, while at the
same time providing for good drainage and aeration

b) Has good CEC capacity and is a small source of NPK at .5-.03-.25 and an average pH of
6.5

c) If not properly leached before packaging and shipment, can contain excess salts, which
are detrimental to most developing seedlings and subsequent growth; leaching of salts
consumes significant quantities of fresh water

d) Sourced in the United States principally from the Philippines, India, Sri Lanka, and
Madagascar, this ingredient has a carbon footprint needing further investigation given
its long distance transport to market

e) Alternatives to coco peat include locally harvested leaf mold, partially decomposed
wood wastes, mushroom compost, and perhaps in the future, dairy waste fiber sourced
from anaerobic digesters

Lecture 4: Soil Media, Fertility, & Container Formats Unit 1.3  |  Part 1 – 121
Propagation/Greenhouse Management

8. Beneficial fungal inoculation

Products such as Rootshield can provide growers with a buffer against fungal pathogens in
soil media

a) Trichoderma fungi, when introduced into soil media, can occupy the physical niche that
might otherwise be occupied by pathogenic fungi that can harm seeds and seedlings

b) Trichoderma fungi can also act as direct antagonists to pathogenic fungi, functioning on
your behalf to keep crops healthy

c) Like other living organisms, fungal inoculants should be protected against degradation
and stored refrigerated to extend their shelf life

d) While human health concerns are limited, basic safety precautions like wearing gloves,
long sleeves, a dust mask and eye protection are all recommended when handling
beneficial fungi, as with all other dry, powdered ingredients

C. Environmental Impacts and Sustainability in Soil Mixes and Media
1. As noted above, many of the most commonly used ingredients in soil mixes come either

from non-renewable or questionably sustainable sources. Selecting soil mixes for container
grown plants is one of the decisions where organic growers often make choices that may
not be fully in alignment with their philosophical principles.
a) Sustainably oriented growers should seek out non-toxic, naturally occurring, non-

extractive, and renewable resources and byproducts of other processes as a starting
point when trying to build soil mix recipes. When less sustainable choices are made, it is
important to use these costly resources wisely in an effort to maximize their efficacy and
reduce your overall environmental impacts.
b) Live, biologically active mixes are principally reliant on diverse soil organisms, in
the presence of water, for pest and disease suppression, for the decomposition of
undigested organic matter in mixes, and for the release of nutrients from the plant and
mineral derived components of the growing media
c) The grower can control the structure and texture of soil mixes, which dictate drainage,
aeration, and moisture retention, when creating or selecting soil media
d) The structure and texture of your growing media, combined with your cultural
practices—frequency of water delivery, temperature regulation, and the management
of air circulation—should work synergistically to foster healthy, steady, and
uninterrupted growth of seedlings as they move toward transplant maturity

2. Storage and handling of soil ingredients and mixes

To maintain the integrity and quality of ingredients and mixes, growers need to take some
basic precautions

a) Protect ingredients from degradation by sun, wind, rain, and extreme temperatures
b) Store ingredients in a cool, well-aerated, rain-free location, away from potential sources

of pathogens and weed seeds infestation. Protecting against these possibilities will go a
long way toward improving crop health, minimizing losses, and reducing labor inputs.
c) Blend mix media in small batches for near-term use:
i. Small batch production is particularly important to maximize the benefits of live,

biologically active ingredients such as the bacteria and fungi present in composts,
and purchased inoculants, e.g., Trichoderma fungi
ii. Long-term storage of large volumes of mix can lead to compaction, loss of structural
properties, and diminished nutrient supply due to volatilization or leaching
iii. If allowed to dry, large volumes of soil can be much more difficult to evenly re-wet for
use in mixes

Part 1 – 122  |  Unit 1.3  Lecture 4: Soil Media, Fertility, & Container Formats
Propagation/Greenhouse Management

D. Supplemental Fertility in the Greenhouse

1. Conditions where supplemental fertility may be necessary or useful

Although organic mixes ideally contain all the fertility needed to sustain steady,
uninterrupted plant growth, there may be times where additional inputs are necessary

a) To compensate for poor quality, nutrient-deficient ingredients, especially immature or
older, poorly stored compost

b) To promote biological activity and nutrient release by supplying nitrogen to the soil
microbial population; microbes use supplemental nitrogen to facilitate the release of
plant-based nutrients from the soil mix

c) To alleviate stress, especially in cell-type containers when plants are past optimal
transplant stage, have become root bound, or are showing signs that previously
available nutrients have been exhausted

d) To stimulate growth, such as when the grower needs to accelerate plant growth for a
specific plant-out date or when seedlings have been contracted for sale and it is clear
that they will not reach salable size quickly enough

2. Potential concerns when using supplemental fertility
a) Water soluble nutrients such as the nitrogen in fish emulsion can easily be leached

out of growing containers and potentially enter local waterways if irrigation is poorly
managed and vegetative buffer strips are not present to preserve water quality (see
Supplement 2, Conserving Water and Protecting Water Quality)
b) Inputs can be expensive, and need to be available on site so that fertility issues can be
quickly addressed
c) Supplemental fertility typically requires substantial additional labor for application
d) Additional application equipment is required; in some cases, additional filtration is
needed if being applied through drip or fine-nozzled spray systems
e) Excess nitrogen application can promote highly nitrogenous, pest-susceptible growth,
which may then lead to using more inputs to control pests
f ) Overreliance on highly soluble nutrient inputs mimics the conventional mindset of
feeding plants directly, with readily available ingredients, rather than building soil
health and biology to promote nutrient release and pathogen resistance

3. Ways to apply supplemental fertility
a) Inputs can be blended into soil mixes at time of mix making. This common strategy

requires advance knowledge of need for additional fertility and is most useful with
medium- to slower-acting meals and powdered ingredients.
b) Powdered, granular, and pelletized ingredients can be “top dressed” on the surface of
container soils. This can be effective with fast- to medium-acting inputs, depending on
the crop life cycle and extent of immediate need.
c) Water soluble inputs are commonly applied as a soil drench as part of a regular
irrigation set, thus becoming a “fertigation.”This is a particularly useful, quick-fix
approach to address immediate nutrient deficiencies or to rapidly increase the rate of
plant growth using readily available, water-soluble nutrients, delivered with irrigation
directly to the root zone.
d) Water-soluble nutrients can also be delivered as foliar sprays, specifically directed at the
leaf undersides where stomata are concentrated to maximize uptake potential

4. Commonly used supplemental fertilizers for soil drenches and foliar application (see
Resources section for sources of OMRI-/NOP-certified supplemental fertilizers)

a) Fish emulsions and soluble fish powders for N-P-K (2-5N-2-4P-0-2K) are regularly used
for both soil and foliar applications. They provide immediately available nutrients to
support growth.

Lecture 4: Soil Media, Fertility, & Container Formats Unit 1.3  |  Part 1 – 123
Propagation/Greenhouse Management

b) Kelp extracts and powders supply micronutrients, naturally occurring growth hormones,
a minor amount of N and up to 4%K, all in a form readily accessible to crops. Care should
be taken using kelp meal extracts in seedling mediums, as too much can stunt plant
growth.

c) Worm castings tea (dilute N-P-K and disease suppression)
d) Compost teas, brewed on farm from high quality composts can provide a dilute source

of N-P-K and micronutrients. By inoculating soil and foliage with beneficial bacteria and
fungi, they can also suppress diseases.
e) As the market for inputs has expanded, a wide array of soluble products has become
available. Growers should consult with others in their area to see what products have
been most valuable and provide the greatest return on investment.

E. Container Formats for Seedling Production (see Appendix 6, Examples of Propagation Containers)
1. Cell/plug type trays: The most common containers for contemporary seedling production.

They are manufactured in a huge array of cell sizes and cell shapes. The key is to match
cell size with root nature of the crop, size of desired transplant, appropriate media, and
available space in the greenhouse. These containers are normally made out of expanded
polystyrene, high density polypropylene ,or polyethylene. Each has advantages and
disadvantages.
a) Advantages of cell/plug trays
i. The close spacing of cells allows growers to maximize plant density in valuable

greenhouse space
ii. Because cell size are relatively small when compared to traditional wooden flat-

grown crops, growers use very little soil media to produce thousands of plants
iii. Because each plant grows individually, in a separate cell, roots do not intertwine and

thus do not have to be separated at time of transplanting
iv. Roots are “air pruned” when they reach the bottom of the cell, in most plug tray

designs, which causes roots to branch higher up and more rapidly fill out the root
ball
v. Because plants with well “knitted” roots that hold the soil ball together can be easily
removed from the plug trays, it is possible to plant most crops with little to no
transplant shock, assuming the grower otherwise uses good transplanting practices
b) Disadvantages of cell/plug trays
i. The small volume of soil used cells/plugs means that each individual plant has
limited access to soil nutrients, thus increasing the likelihood growers will have to use
supplemental fertility to keep plants growing strong or to hold them if transplanting
time is delayed
ii. Small cells have limited root runs, which shortens the window of opportunity for
optimal transplant timing, again leading to the potential need for supplemental
fertility
iii. The small volume of soil means that growers will have to water more frequently to
compensate for the rapid soil drying that is likely when temperatures are hot and
plug sizes are small
iv. Some flat bottom cell designs drain poorly and actually hold water at the bottom
of the cell. This “perched water table” can be problematic for crop roots sensitive to
rotting or those needing abundant oxygen throughout the root zone.
v. Some round cell designs can promote “root spiraling,” causing plants to become root
bound early in their development

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Propagation/Greenhouse Management

vi. Cell/plug trays are currently all manufactured from non-renewable sources and even
when recyclable, their manufacture, recycling and eventual disposal have high life
environmental footprints (see Appendix 8, Environmental Impacts of Cell/Plug Trays)

2. Traditional wooden flats, though seldom used in contemporary greenhouse and on-
farm production systems, have many valuable characteristics as well as several inherent
disadvantages

a) Advantages of wooden flats for propagation
i. By growing plants at a relatively low density, this format provides a very large root

run. This expanded resource base can grow large, vigorous starts resistant to pest and
disease pressure and tolerant of weather variables.
ii. Substantial nutrient supply per plant means that plants have plenty of nutrients to
grow steadily and without interruption
iii. Substantial soil volume per plant also means growers will have to deliver water less
frequently.
iv. The large soil volume and nutrient supply gives growers a long window of
opportunity to transplant while crops are still in their prime, even if soil or weather
conditions delay planting beyond what would normally be acceptable for cell/plug-
grown crops
b) Disadvantages
i. This format consumes large volumes of soil media, thus increasing production costs
for both labor and materials
ii. Lower plant density afforded by typical spacing in wooden flats means that precious
greenhouse space may not be being used to optimum capacity
iii. Flats filled with well-watered mix, especially mixes that use substantial quantities of
compost, sand, or soil can be very heavy, requiring more labor, and increasing the risk
of lower back injuries
iv. Because roots all grow together in the open flats, this format has much greater
potential for root disturbance and transplant shock even with the most delicate
handling, when individual plants and roots are separated from the inevitable
intertwined root mass.

Lecture 4: Soil Media, Fertility, & Container Formats Unit 1.3  |  Part 1 – 125
Propagation/Greenhouse Management

Part 1 – 126  |  Unit 1.3 
Propagation/Greenhouse Management

Demonstration 1: Greenhouse Management
for the instructor

OVERVIEW PREPARATION AND MATERIALS
• A working greenhouse structure where the essential
This demonstration provides
students with an understanding management tools and techniques can be discussed and
of the working components of the demonstrated
greenhouse facility and the tools • Thermometer and Appendix 12, Greenhouse Records
available to manage environmental Sheet, to show current conditions and records of recent
conditions that best meet the needs temperature fluctuations
of pre-emergent and seedling • Thermometers positioned in different microclimatic zones
crops in the facility. Students (if applicable) to show how differences can be used to meet
should become familiar with the different plant needs under a single management regimen
fundamental skills and concepts to
create ideal growing conditions, such PREPARATION TIME
as temperature and air circulation 1 hour
management.
DEMONSTRATION TIME
1 hour

DEMONSTRATION OUTLINE

A. Managing Greenhouses

1. Discuss and demonstrate orientation of greenhouse
(i.e., solar aspect)

2. Discuss and demonstrate methods for air circulation via
venting, fans, etc.

3. Discuss and demonstrate temperature management
a) Ideal temperature ranges (see Appendix 3)
b) How heat is retained
c) The use of thermal mass in heat retention
d) Techniques for evaporative cooling
e) The role of venting in maintaining ideal temperature,

humidity, and gas exchange
f) Active heating systems

4. Use of microclimates within greenhouse
5. Discuss and demonstrate record keeping in the

greenhouse (see Appendix 12)
a) Date
b) Previous high/low
c) Current temperature
d) Weather description
e) Description of environmental conditions in

greenhouse
f) Management actions taken

Instructor’s Demonstration 1 Outline Unit 1.3  |  Part 1 – 127
Propagation/Greenhouse Management

Demonstration 2: Propagation Media
for the instructor

OVERVIEW PREPARATION AND MATERIALS
1. Have both wet and dry samples of several possible
Students will examine both
unblended propagation ingredients raw ingredients that are used in propagation media:
and the completed propagation Compost, soil, sand, perlite, vermiculite, composted
media. By looking at the individual wood chips, grape seed pumice, peat moss, and coir
ingredients, finished propagation fiber, etc.
media, and typical garden soils in
containers, students will see the 2. Have wet and dry samples of the media commonly used
components of propagation media in your operation and perhaps others such as the Cornell
that are critical to creating proper Peat Lite Mix and the UC Potting Mix (see Resources
drainage, aeration, and moisture section) and/or commercial propagation media for
retention. The instructor should comparison
also emphasize the importance of
proper moisture in propagation 3. Assemble necessary tools (flat head shovels,
media so that root-to-soil and/or wheelbarrows) and hoses to supply moisture
seed-to-soil contact can be achieved
with only minimal additional 4. Assemble ingredients to make the desired mix of
water inputs. Instructors should be ingredients
certain to discuss the importance
of proper storage and handling PREPARATION TIME
of media to maintain fertility and 1.5 hours
protect against contamination by
pathogens. DEMONSTRATION TIME
1.5 hours

DEMONSTRATION OUTLINE

A. Propagation Media
1. Review desirable characteristics of propagation media
2. Review individual media constituents and properties

imparted by each
a) Show ingredients that provide nutrients (N, P, K, and

micronutrients)
b) Show ingredients that promote drainage and aeration
c) Show ingredients that serve to retain moisture
3. Demonstrate the techniques of blending materials to

create homogenized media
4. Assess and adjust media for appropriate moisture
5. Discuss use and proper storage techniques for

propagation media

Part 1 – 128  |  Unit 1.3  Instructor’s Demonstration 2 Outline
Propagation/Greenhouse Management

Demonstration 3: Sowing Seed
for the instructor

OVERVIEW PREPARATION AND MATERIALS
1. Assemble a selection of different cell/plug trays
In this demonstration students
should observe and participate in 2. Assemble wooden flats suitable for seed sowing
sowing a variety of different seed
types and sizes in both cell trays and 3. Bring both large (sunflowers, squash, etc.) and small
wooden flats. Students will review seeds (lettuce, larkspur, snapdragon, etc.) to illustrate the
the advantages and disadvantages range of seed sizes
of each format and why certain
crops may be better suited to a 4. Bring any mechanical seeding devices such as sliding
particular method. In this session, a plate seeders and seeds appropriate to their use
discussion and look at various seed
sizes will illustrate the importance of PREPARATION TIME
sowing seeds to appropriate depths 1 hour
to ensure a high percentage of
germination and seedling survival. DEMONSTRATION TIME
1 hour

DEMONSTRATION OUTLINE

A. Seed Sowing Techniques
1. Demonstrate container-filling techniques
2. Discuss the advantages and disadvantages of each

container format
3. Demonstrate sowing and coverage techniques
a) Discuss and demonstrate techniques for broadcasting

and drilling seed into flats, including proper depth
b) Discuss the significance of seed density as it relates to

potential future competition and timing of pricking
out
c) Discuss and demonstrate sowing by hand into cell
type trays
d) Discuss and demonstrate sowing into cell trays with a
sliding plate seeder or other mechanisms
4. Discuss labeling and record keeping and their
importance in maintaining variety distinctions, trouble
shooting, and future crop planning (see Appendix 11)
5. Discuss and demonstrate watering-in techniques
6. Discuss and demonstrate optimal min/max germination
temperatures (see Appendix 3)
7. Discuss days to germination at varying temperatures
(see Appendix 4)
8. Discuss and demonstrate optimal post-germination
growing temperatures for seedlings (see Appendix 5)

Instructor’s Demonstration 3 Outline Unit 1.3  |  Part 1 – 129
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Demonstration 4: Transplanting or “Pricking Out”
for the instructor

OVERVIEW PREPARATION AND MATERIALS
1. Have plants available for visual inspection that only
This demonstration illustrates the
technique of transplanting immature show taproot development
seedlings from a high-density flat
format to a lower-density format. 2. Gather plants that have initiated a branched root system
The importance of doing this work suitable for pricking out
under appropriate environmental
conditions (low light levels, low 3. Have plants showing signs of overdevelopment that
temperatures, high relative humidity, would make pricking out more difficult
and still air/low wind velocity)
cannot be overemphasized. Students 4. Have undersown (very low-density) flats to illustrate
will have the chance to look at plant inefficient use of space as well as the wider window
development and its relevance to of opportunity possible when young plants are not
successful transplanting or “pricking competing for resources
out” in the greenhouse setting. Be
sure to emphasize the significance of 5. Have oversown flats illustrating the effects of
seedling density and proper timing competition and the imperative of moving swiftly to
of pricking out to prevent undue prevent disease and alleviate the effects of nutrient stress
competition for resources and to
prevent diseases. 6. Have flats sown at appropriate density to demonstrate
best use of space and proper timing for movement.

7. Have plants of basal rosette nature (e.g., statice,
Limonium sinuatum) and upright nature (e.g.,
snapdragons, Antirrhinium majus) to discuss and
demonstrate appropriate planting depth relative to
seedling architecture and physiological adaptations such
as adventitious rooting

PREPARATION TIME
1 hour

DEMONSTRATION TIME
1.5 hours

Part 1 – 130  |  Unit 1.3  Instructor’s Demonstration 4 Outline
Propagation/Greenhouse Management

DEMONSTRATION OUTLINE

A. Transplanting and Pricking Out Techniques (see Appendix 9)
1. Review/discuss environmental conditions appropriate to plant handling
2. Discuss and demonstrate stages of plant development appropriate for pricking out
3. Discuss and demonstrate plant root systems appropriate for pricking out
4. Discuss and demonstrate the significance of seedling density relative to timing of

pricking out
5. Discuss and demonstrate proper/gentle handling techniques when dealing with young/

easily injured seedlings
6. Discuss and demonstrate techniques for watering-in transplants
7. Discuss labeling and record keeping and their importance in maintaining variety

distinction, trouble shooting, and future crop planning (see Appendix 11)
8. Discuss considerations for post-transplant care

Instructor’s Demonstration 4 Outline Unit 1.3  |  Part 1 – 131
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Demonstration 5: Greenhouse Irrigation
for the instructor

OVERVIEW PREPARATION AND MATERIALS
• All irrigation equipment commonly used in the propagation
In this demonstration, students
will learn about the various tools facility (e.g., hoses, watering cans, fixed spray nozzles,
and techniques used to deliver irrigation timers and solenoid control valves, mist systems,
water to pre-emergent seeds and etc.)
seedlings in a given propagation
facility. Emphasis should be placed • Recently sown seeds in flat and cell tray format
on creating optimal soil moisture
conditions to facilitate healthy plant • Seedlings in flat and cell tray format
growth through proper irrigation
frequencies and volumes of water PREPARATION TIME
applied. You should also discuss the 1 hour
advantages and disadvantages of the
systems and tools used. DEMONSTRATION TIME
1 hour

DEMONSTRATION OUTLINE

A. Irrigating Seeds and Seedlings
1. Discuss and demonstrate irrigation techniques prior to

seedling emergence with attention to the differences in
wet-to-dry swing for large- and small-seeded crops

2. Discuss and demonstrate irrigation techniques used for
post-seedling emergence and early seedling development

3. Discuss the typical changes in frequency and volume of
water delivered during seedling development (i.e., from
pre-germination—frequent, shallow applications—to
lower frequency, greater volume of water supplied as
seedlings mature)

4. Discuss and demonstrate any necessary adjustments
needed based on germination, disease or pest problems,
and/or plant growth observations

5. Emphasize the importance of paying extra attention
to corners and edges of greenhouse; these are often
overlooked

Part 1 – 132  |  Unit 1.3  Instructor’s Demonstration 5 Outline
Propagation/Greenhouse Management

Demonstration 6: Seedling Development & the
“Hardening Off” Process
for the instructor

OVERVIEW PREPARATION AND MATERIALS
• Seedlings at varying stages of maturity
This demonstration shows students
how to prepare seedlings for field PREPARATION TIME
transplanting. 0.5 hour

DEMONSTRATION TIME
0.5 hour

DEMONSTRATION OUTLINE

A. The Hardening Off Process
1. Define the hardening off process and its role in seedling

maturation and survival
2. Discuss characteristics of seedling maturity (see

Appendix 10)
3. Discuss regional importance and influence on duration

of hardening off process. Greater temperature
differences between greenhouse and field conditions will
require a longer hardening off period.
4. Discuss and demonstrate the various propagation
structures and techniques used in the hardening-off
progression
a) Highly controlled environment of greenhouse settings
b) Partially moderated conditions: Hoophouses
c) Outdoor benches approximating field conditions
5. Provide examples of seedlings prepared for transplanting

Instructor’s Demonstration 6 Outline Unit 1.3  |  Part 1 – 133
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Part 1 – 134  |  Unit 1.3 
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Assessment Questions

1) List two pre-conditions that must be met for seed germination and four environmental conditions
that must be achieved for optimal seed germination.

2) What is the optimal average daytime temperature range that should be maintained in the
greenhouse for the germination and early growth of most annual vegetables and cut flowers? What
would be the minimum nighttime temperature?

3) List four advantages of the use of greenhouse-raised transplants over direct seeding of crop plants.
Describe two disadvantages.

4) Why is the careful selection of crop varieties important?

5) What are four important qualities of a propagation mix? List two propagation mix constituents that
may be used to assure each of the previously listed qualities.

Assessment Questions Unit 1.3  |  Part 1 – 135
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6) What pieces of information are commonly documented in the propagation process and why?

7) What is the “hardening off” process?

8) List two characteristics of cell-tray-grown seedlings at transplanting maturity.

9) List two necessary steps for preparing seedlings before transplanting them to the field or garden.

10) List the environmental conditions most favorable for successful bare-root transplanting/ pricking out
seedlings grown in a flat format.

11) Describe four preventive measures and two active measures used to control fungal plant pathogens
in greenhouse facilities.

Part 1 – 136  |  Unit 1.3  Assessment Questions
Propagation/Greenhouse Management